Double-sided wafer scrubber with a wet submersing silicon wafer indexer

ABSTRACT

An embodiment of the present invention is a wet indexer for receiving a cassette of wafers from a previous processing station that have not been allowed to dry. The wet indexer then keeps the wafers submersed in processing solution before and during indexed transmission to later cleaning stations.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to semiconductor fabricationequipment and more specifically to wafer manufacturing, postchemical-mechanical planarization cleaning and particle monitor waferreclaiming.

2. Description of the Prior Art

Semiconductor processing depends on clean wafers and therefore a cleanenvironment within which to process the wafers. Two methods areconventionally used to obtain clean wafers. A first method includespreventing particulate contamination from occurring, such as doing thewafer processing in a class one hundred cleanroom or a class tencleanroom. A second method cleans wafers that are dirty, typically witha rinser-dryer. No amount of particulate contamination prevention willkeep all wafers clean because some process steps actually generateparticulates. Therefore, cleaning of contaminated wafers is almostalways necessary.

Double-sided scrubbers, e.g., the OnTrak Systems, Inc. (Milpitas,Calif.) Systems DSS-200 and DSS-150, are directed at applications thatrequire a thorough cleaning of both sides of a wafer. Such systems arebeing used in semiconductor fabrication (Fab) lines around the world forprocesses as diverse as bare silicon cleaning by silicon materialsuppliers to post chemical-mechanical planarization (CMP) forinter-metal dielectric planarization cleaning.

The demand for ever flatter inter-metal dielectrics has increased assemiconductor device geometries continue to shrink. CMP produces a moreplanar dielectric layer between metal layers by using a silica slurryfor a chemical part of the process. If the slurry is not thereaftercompletely removed, or if it is allowed to dry, so many defects willoccur in the individual circuit dice that the whole wafer may have to bescrapped, thus lowering yields and raising unit manufacturing costs.

A conventional double-sided scrubber system has two brush stations thatallow for a more thorough cleaning of wafers. A spin station is used torinse and dry both sides of a wafer without contacting the wafersurfaces. A robot is included that grips cleaned wafers on the edges andplaces each wafer on a blade that lowers into a wafer cassette. Thecassette is positioned on its back to allow a laminar air flow throughthe cassette. The brushes are constantly flushed with deionized water toinhibit particle buildup. An indexer accepts a cassette of wafers from aprevious operation, such as polishing, and will transmit a wafer fromthe cassette to the cleaning, rinsing and drying stations whenappropriate.

SUMMARY OF THE PRESENT INVENTION

It is therefore an object of the present invention to provide asemiconductor processing device that will clean and/or keep cleansemiconductor wafers.

It is a further object of the present invention to provide asemiconductor processing device that prevents semiconductor wafers fromdrying between processing steps.

Briefly, an embodiment of the present invention is a wet indexer forreceiving a cassette of wafers from a previous processing station thathave not been allowed to dry. The wet indexer then keeps the waferssubmersed in processing solution before and during indexed transmissionto later cleaning stations.

An advantage of the present invention is that it provides a system thatdoes not allow the wafers received from a previous process step to dry,thus making the job of cleaning easier and more efficient.

These and other objects and advantages of the present invention will nodoubt become obvious to those of ordinary skill in the art after havingread the following detailed description of the preferred embodimentwhich is illustrated in the various drawing figures.

IN THE DRAWINGS

FIG. 1 is a schematic diagram of a double-sided scrubber system with awet indexer according to the present invention;

FIG. 2A is a cross-sectional view of the front of the wet indexer of thesystem of FIG. 1;

FIG. 2B is a cross-sectional view of one side of the wet indexer of thesystem of FIG. 1; and

FIG. 3 is a perspective exploded assembly view of the wet indexer of thesystem of FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 illustrates a double-sided wafer scrubber system 10 comprising awet indexer 12 for receiving a cassette 14 with a plurality of wafers 16from a previous processing station 18 and for keeping the wafers 16submersed in a tank 20 of a process solution 21 before and duringindexed transmission to later stations, a pair of brush stations 22 and24, a spin-dry station 26 and a robotic receiver transfer station 28.Process solution 21 may comprise deionized water, for example. A track30 draws wafers 16 pass a pair of brushes 32 and 34 to a spinnerassembly 36 where a robotic arm 38 lifts each finished wafer 16 out fromthe station 26. Wafers 16 are typically round, 100 millimeters to 300millimeters in diameter (e.g., four inches to twelve inches).

Brushes 32 and 34 are direct drive brushes and each of brush stations 22and 24 has two top and two bottom spray nozzles (not shown) to transportwafers 16 along a wet track 30 and a scrubbing solution spray nozzle(not shown). For more information concerning the transporting of wafersby fluid means, see, U.S. Pat. Nos. 4,874,273, issued to Tokisue, and,3,976,330, issued to Babinski. The spray nozzles may comprise anon-sticking material, e.g., TEFLON. Track 30 helps keep wafers 16 wet,which makes cleaning of particulates from the wafers easier. The spraynozzles are preferably independently controllable. Brushes 32 and 34have hollow cores and are supplied with a flow of deionized water duringoperation for continuous rinsing of the brush bristles. The deionizedwater is preferably ultrapure, eighteen megohm. The constant flushing ofbrushes 32 and 34 serves two purposes. First it prevents particlebuild-up on the brushes, and second, it keeps the deionized waterflowing thereby preventing bacteria growth within the system plumbing.Nylon or PVA may be used for brushes 32 and 34.

Preferably, the process solution (e.g., deionized water) flows as longas power is being applied to system 10. Brush station 24 includes anoptical wafer-flat sensor 40 to properly align wafers 16 for spin-drystation 26. The sensor 40 helps minimize vibration which, in turn,minimizes particulate generation due to the wafer flat being misaligned.A reflective sensor 42 is included in spin-dry station 26 to identifywhen a wafer 16 enters. After a wafer 16 stops along track 30 withinspin-dry station 26, spinner assembly 36 rises to pickup the wafer.Preferably, the plumbing of station 26 allows for both top and bottomrinse lines. An open four-finger nest assembly 41 allows deionized waterto contact both sides of wafers 16. The tops and bottoms areconventionally dried simultaneously by spinning. Preferably, counterbalances are included on the nest assembly 41 to prevent opening of thefingers during spinning. After spinning, wafers 16 are raised fortransfer by robotic arm 38.

Robotic arm 38 grips wafers 16 at three points around the outside edgeand places the clean, dry wafer on a blade that lowers the wafers 16into a receiver cassette 44. The receiver cassette is preferablyhorizontally positioned to allow the wafers 16 to be lowered into theirrespective slots. A laminar air flow is directed continually throughcassette 44.

FIGS. 2A, 2B and 3 illustrate wet indexer 12, which comprises the tank20, a wafer outlet 50, a cover 52, a bottom wafer guide 54, a manifold56, a wafer-present optical sensor 58, a pair of nozzles 60, a cassetteplatform 62, a cassette-present optical sensor 64, a lift arm 66, a leadscrew 68, a support block 70, a belt drive 72 and a stepper motor 74.Tank 20 is filled with a processing solution 21, such as water (shown inFIG. 1 only for clarity). Wet indexer 12 is constructed such that wafers16 are not contacted when dry by belts that are typical of the prior artand that can leave skid residues on the surface of the wafer thuscontacted. Bottom wafer guide 54 is therefore a non-wafer-contactingelement. The elements of wet indexer 12 that can come in contact withthe processing solution 21 are preferably comprised of non-metallicmaterials or have non-metallic coatings on at least the surfaces thatcan come in contact with the processing solution 21. Such a use ofnon-metallic materials is for preventing a contamination of wafers 16with ions of the respective metals involved.

In operation, a user places cassette 14 (FIGS. 2A and 2B) on platform 62which is in a raised position nearly level with outlet 50. Sensor 64detects that cassette 14 is present and stepper motor turns lead-screw68 to lower arm 66 and platform 62 to submerse wafers 16 in processingsolution 21. When a wafer 16 is needed in station 22 (FIG. 1), steppermotor turns lead-screw 68 to raise arm 66 and platform 62 such that awafer 16 is aligned with outlet 50. Deionized water is sprayed fromnozzles 60 to move wafer 16 through outlet 50 and between guides 52 and54. If sensor 58 does not detect a wafer 16 at an appropriate timepoint, the flow of water from nozzles 60 is preferably inhibited toprevent damage to brush 32 (FIG. 1). Processing solution 21 acts as apre-soak and prevents drying of wafers 16 while they are queued up forcleaning. All components or surfaces of components within wet indexer 12that come within contact of processing solution 21 are preferablycomprised of non-metals, e.g., plastics, PVA, and TEFLON. Nozzles 60 arepreferably comprised of a material that produces a non-diffused spray.Sensor 64 includes fiber optic cable that is routed up and out of tank20 along arm 66 to an LED and light detector that remain dry. Manifold56 is supplied a flow of deionized water that tends to float any wafers16 passing above in guides 52 and 54.

A process embodiment of the present invention includes the steps ofpreventing the drying of wafers delivered to a wafer cleaning system andindexing the wafers for cleaning from a queue submersed in a volume ofprocess solution, such as deionized water. In FIG. 1, a boat filled withprocess solution is preferably used when transporting wafers 16 andcassette 14 between previous processing station 18 and indexer 12 toprevent drying of wafers 16. By not allowing the wafers to dry beforecleaning, subsequent cleaning steps are improved because the otherwiseunavoidable bonds between particles and the waters are prevented orinhibited. Small diameter particles, which can form particularly highenergy adhesion bonds, are therefore not able to become a source oftrouble the later cleaning stages. Problems with small particulatesgenerated in previous fabrication processes that have not yet bonded tothe wafers are thereby avoided.

Although the present invention has been described in terms of thepresently preferred embodiments, it is to be understood that thedisclosure is not to be interpreted as limiting. Various alterations andmodifications will no doubt become apparent to those skilled in the artafter having read the above disclosure. Accordingly, it is intended thatthe appended claims be interpreted as covering all alterations andmodifications as fall within the true spirit and scope of the invention.

What is claimed is:
 1. A wet indexer, comprising:a tank for holding aprocessing solution and for accepting a cassette of wafers from aprevious processing station and for pre-soaking said wafers in saidprocessing solution while said wafers are in a queue waiting fortransfer to a subsequent stage; wafer outlet means in a side of the tankfor a non-contacting passing of individual said wafers out of the tank;and liquid jet means for motivating individual said wafers to pass fromsaid cassette and out through the wafer outlet means.
 2. The indexer ofclaim 1, further comprising:wafer-present sensor means for detectingindividual said wafers passing through the wafer outlet means whereinthe liquid jet means may be operated appropriately to motivate saidindividual wafers.
 3. The indexer of claim 1, furthercomprising:cassette platform and platform elevation means for holdingand indexing said cassette of wafers and for submerging said cassette ofwafers in said processing solution and for lifting said cassette ofwafers out of said cassette of wafers out of said processing solution.4. The indexer of claim 3, further comprising:a cassette-present sensorfor detecting whether or not said cassette of wafers is being held bythe cassette platform and platform elevation means wherein operation ofthe cassette platform and platform elevation means may be disabled if acassette is not present.
 5. The indexer of claim 3, wherein the cassetteplatform and platform elevation means comprises:a lift arm; a lead screwattached to the lift arm; and a stepper motor coupled to the lead-screwfor moving said cassette of wafers up and down within the tank.
 6. Theindexer of claim 1, wherein the wafer outlet means comprises:anon-wafer-contacting wafer guide; a manifold for floating of said waferspassing through the wafer guide with a processing solution such that theliquid jet means moves said individual wafers out through the waferguide.
 7. A wafer cleaner system including a plurality of stations,comprising:a wet indexer for receiving a cassette of wafers from aprevious processing station and for keeping the wafers submersed in atank of processing solution before and during an indexed transmission toa next station, the wet indexer including processing solution jet meansfor extracting said wafers from said cassette and for moving said wafersthus extracted to said next station; a first wafer brushing station forreceiving said wafers from the wet indexer and for cleaning said waferson both sides with processing solution; a second wafer brushing stationfor receiving wafers from the first brushing station and for cleaningsaid wafers on both sides with processing solution; a wafer spin-drystation for receiving said wafers from the second brushing station andincluding spinning means for spin-drying said wafers; and a roboticreceiver transfer station for receiving said wafers from the waferspin-dry station and for placing said wafers in a cassette.
 8. Thesystem of claim 7, wherein:the wet indexer includes cassette-presentdetection means for enabling a lowering said cassette into said tank ofprocessing solution only when, a cassette is present; said processingsolution jet means comprises liquid jet nozzles and wafer-presentdetection means to shut-off a flow of processing solution through saidnozzles when a wafer is not present; and the second wafer brushingstation includes an optical wafer-flat sensor to properly align saidwafers for the wafer spin-dry station.